1. Field of the Invention
The present invention relates to a process for making an elastic stitchbonded fabric by multi-needle stitching a nonbonded or lightly bonded fibrous layer with elastic yarns. More particularly, the invention concerns an improvement in such a process wherein the elastic stitching yarns enter the needles with high residual stretch. The process provides more economical, stretchable fabrics, particularly suited for use in elasticized portions of diapers, cuffs, waistbands, bandages, and the like.
2. Description of the Prior Art
Processes are known for making stretchable stitchbonded nonwoven fabrics by multi-needle stitching of a fibrous layer with elastic yarn. Several of my earlier patents disclose such processes. For example, U.S. Pat. No. 4,704,321 describes such stitching of a plexifilamentary polyethylene sheet (e.g., Tyvek.RTM.); U.S. Pat. No. 4,876,128 discloses such stitching of other fibrous layers; and U.S. Pat. No. 4,773,238 describes such stitching of a substantially nonbonded web and then contracting the stitched fabric to less than half its original area.
To produce a highly stretchable stitchbonded fabric by a process of my earlier patents generally required that the stitched fabric be allowed to contract extensively immediately after the stitching step. The contraction was caused by the retractive power of the elastic stitching yarns. Although my earlier processes produced stitchbonded fabrics suitable for a variety of uses, reductions in fabric cost were desired. The cost per unit area of elastic fabrics produced by my earlier processes were in direct proportion to the area contraction the fabric experienced immediately after stitching. Thus fabrics with high post-stitching contraction had high costs per unit area.
In the past, stitchbonding with elastic yarns usually was not performed with accurately controlled tensions on (a) fibrous layers fed to the stitchbonding machine, (b) elastic yarns fed to the stitching needles and (c) stitched fabrics leaving the machine. Generally, the stitchbonding machines were operated with high tensions on each of these components. In addition, the elastic yarns were subjected to increase tension by the action of the stitching needles of the stitchbonding machine. Accordingly, the yarns arrived at the stitching needles with high elongations and were inserted into the fibrous layer very little residual stretch remaining in the yarns. The elongation of the stitched yarn usually was quite close to its break elongation. For example, in accordance with the processes described in my U.S. Pat. No. 4,773,238, the elastic yarns were fed to the stitchbonding machine with an elongation of 100 to 250%, and then further stretched by the action of the stitching needles. The high elongation and low residual stretch of the elastic yarns in the stitched fabric were evident from the large contraction the stitchbonded fabric experienced as it left the stitching machine, even though a high wind-up tension was applied to the exiting fabric, and from the inability of the resultant fabrics to be stretched much beyond its original stitched dimensions. In Example 2 of the patent, a maximum extension to 20% beyond the original length of the fibrous layer was disclosed; all other examples disclosed fabrics that could not be stretched beyond their original stitched length. The high tensions and retractive forces in the stitching yarns of the earlier processes resulted in contractions of the stitched fabric to less than 40% and sometimes to than less than 20% of their original stitched dimensions. It was only after the contraction that the fabrics could be stretched significantly.
An object of the present invention is to provide an improved process for making an elastic stitchbonded fabric which does not require a large contraction of the fabric immediately after stitching in order to achieve elastic stretchability.